It is a requisite to de-ice the accumulation of frost, ice and snow or combinations thereof on the wings of aircrafts to restore the natural shape of the wings by removing any frost, ice or snow build-up that distorts its shape and to permit proper functioning of the ailerons Ice, frost or snow also adds to the weight of the aircraft, thereby impeding flight. The removal of frost, ice or snow is effected by spraying a de-icing glycol solution to cause the frost, ice or snow to melt away and protects the aircraft for sufficient time after de-icing against further precipitation. The concentration of glycol in the solution varies according to climatic conditions. Such solutions typically comprise glycol, water, and minor amounts of additives such as surfactants, and a corrosion inhibitor.
After spraying the de-icing solution on the aircraft, the solution becomes diluted with water from melted frost, ice and snow and becomes contaminated with pollutants present on the tarmac area where aircraft propagate to be de-iced. These areas are usually concrete areas polluted with sand, abraded rubber from aircraft tires, oil, combustion residue, fumes from the aircraft, deicing salts, grit, traces of fuel, solid debris such as grass and leaves, and chemicals found in concrete. In the past, such waste glycol solutions where harnessed in reservoirs or vacuum trucks for disposal and treatment at remote sites for disposal. Such a practice proved to be a burden on the environment and resulted in the loss of glycol which is an expensive product. Typically, the airport assumes the cost of this disposal and by recovering the spent glycol substantive savings is passed on to the airport facility.
Over the last decades, efforts have been made to recycle glycol residue from aircraft de-icing solutions and various recovery systems have been placed in operation using various methods such as aerobic digesters, cyclone separators, chemical cleaning techniques using absorption and ion exchangers, percolation towers, distillation and stripping columns or towers, etc. However, the operation of some of these have proven problematic and very costly and some have not achieved the desired sought after result of recovering glycol of sufficient purity comparable to purchased virgin glycol, for recycling for use in an aircraft deicing glycol solution. Some of the known techniques have claimed to recycle such glycol solutions to a purity of 99.5% but many have failed to produce this purity. Examples of known techniques can be found, for example, in the patent literature with reference to U.S. Pat. Nos. 5,904,321; 5,411,668; 7,713,319; 8,252,149; US Patent Application Publications 2011/0263909 and 2013/0190539, as well as Canadian Patents 2,116,827 and 2,223,922. Another publication on the topic of recycling glycol from airport tarmacs can be found in an article entitled “A Tour Of The Munich International Airport's Deicing Recycling Plant”, such article being accessible on the web at http://www.aviationpros.com/article/10616425.